PROJECT SUIVIIVIARY (See instructions): Our long-term goal is to study the regulation of immune responses under normal and diseased conditions, particularly the involvement of protein ubiquitination pathway in lymphocyte development, activation, and tolerance induction. Cbl-b is composed of an N-terminal tyrosine kinase binding domain, a RING finger, and C-terminal proline-rich sequences. Genetic studies using Cbl-b deficient mice have shown that Cbl-b is critical in T cell activation, and loss of Cbl-b results in increased autoimmunity. Cbl-b functions as RING-type E3 ubiquitin ligase to promote ubiquitin conjugation to critical signaling molelcules and affects their biological functions. More importantly, we showed that Cbl-b is upregulated during T cell anergy induction and controls the tolerigenic process, thus linking protein ubiquitination pathway to the T cell tolerance. We have recently obtained some unexpected and novel observations. Particularly, we found that Cbl-b is involved in the regulation of Foxp3 expression in inducible regulatory T cells (iTregs) via modulating a novel signaling pathway directly acting at the transcriptional regulation of Foxp3 gene. The new findings form a strong basis for us to hypothesize that Cbl-b plays an essential role in controlling immune responses via promoting protein ubiquitination. In this proposal, we will plan: 1) to investigate the molecular mechanisms by which Cblb E3 ubiquitn ligase regulates Foxp3 gene transcription via modulating Foxo3a-directed gene transcription and to perform genome-wide gene profiling of Tregs to understand the molecular regulation of epigenetic control in Tregs; 2) to examine the in vivo function of iTregs in mouse models of autoimmunity and airway inflammation. These studies will significantly advance our understanding ofthe molecular mechanisms governing Foxp3 gene transcription and ITreg-mediated immune regulation. Such knowledge will eventually facilitate the design of novel therapeutic approaches for cancer, autoimmune and allergic diseases.